T-3

Physics Frontiers Opened by Burning Plasmas
燃焼プラズマが切り開く物理
Yutaka Kamada
鎌田裕Japan atomic Energy Research In stiturte, Naka Fusion Research Establishment,
801-1, Mukouyama, Naka-machi, Naka-gun, Ibaraki-ken, 311-0193, Japan
日本原子力研究所

那珂研究所

311-01 茨城県

那珂郡那珂町

向山 801-1

The nuclear fusion research is now ready to challenge demonstration of the burning plasma
utilizing ITER. From the physics point of view, the burning plasma system is characterized as thenonlinear self regulating combined / complex system. In order to realize the nuclear fusion energy,we need to understand and control this burning plasma system. At the same time, this research area
gives us an opportunity to open physics frontiers. This presentation introduces the key aspects of theburning plasmas in the magnetic fusion research.
1. Self-regulating System

neoclassical transport determines the pressure

The first important aspect is that theprofile. The pressure profile determines the self

burning plasma is a highly self-regulating

generated bootstrap current profile ( thus thesystem. In the burning plasmas, a large amountmagnetic field line structure) and, at the sameof the heating power is generated by so called

time, the radial electric field and the plasma

self-heating. The DT fusion reaction produces

rotation profile. The produced equilibrium

high energy alpha particles, and the alphadetermines the microscopic and macroscopic

particles transfer their kinetic energy to thefluctuations

background thermalized plasmas with theelectrostatic) in the real and velocity spaces,

typical temperature of ~ 10keV. The plasma

and alters the transport again. As the results oftemperature,arethis parameter linkage (Fig.1), the plasma

determined basically by the balance of heating

reaches a new equilibrium. In this self-and diffusion. The diffusion processes show

regulating linkage, the key points appearing inboth continuous and bifurcational (such as H-

the burning high pressure plasma is that themode transition, generation of internal transportlarge fractions (>70%) of the heating power

barriers

and the plasma current is generated by theetc.)

density

anddynamics

andpressure

producesacharacteristic spatial structure of the plasma
kinetic parameters following a global loop of
the parameter linkages. Simply speaking, theplasma itself.

(bothelectromagneticand

Particle Control
external
recyclingheatingCurrent
Profileexternal
flow drive

ionsneutral
impuritie

Pressure
profileFlow & Electric Field
profilemain plasmapedestal plasma

SOL/ divertorplasma

Fig.1 Parameter linkages in the burning plasmas
2. Combined Complex System

MHD / turbulence(~ micro second), parallel

The second point is that the burning plasmaand perpendicular transport time (~ms -is the combined / complex system. i) Lookingsecond) , plasma current profile growth timeat the physics phenomena, fluctuations in(second - 10 second) to the wall saturation timeelectrons / ions and MHD instabilities exhibit(10 sec. - min. / hr.) .

collective nonlinear behaviors. ii) As for the

3. High Energy Particle Physic s

global structure, the confined plasma system

In the burning plasmas, another importantconsists of multiple plasma regimes; 10keV-and new aspect is that a large amount of highclass of the core plasma, keV-class pedestal

energy particles (alpha particles) are produced

plasma, and eV-class divertor plasma. Theseand these energetic ions can kick instabilities

plasma regimes are connecting to each otherdue to wave-particle interactions. In toroidal

but governed by different dominant processes

magnetic configuration system, the Alfvén

with different origin and time constant. For

wave appears as an eigenmode in a frequency

example,its

gap induced by the toroidicity, which is similar

dynamics are determined by both the plasma

to the band gap in the semiconductor. This typeprocess and the atomic process. The scaleof Alfvén wave is called as TAE. The TAE

length of the pedestal parameters are in themodes,

same order of the ion orbits and the penetrationenergetic ions and causes diffusion of thedepth of the neutrals. Furthermore, the spatial

energetic ions. Since the plasma heating power

distribution of the pedestal parameters andstrength and profile is largely affected by thebehaviors show two or three dimensional

alpha particle heating distribution, a feedbackstructures. iii) The time scales of the leading

control schemes for the energetic particle

phenomena span from the growth time of ideal

distribution is an important challenge.

thepedestalstructureandonce

destabilized,

interactwith